United are interested in the Argentina international and reportedly bid 16 million pounds for the World Cup finalist, who seemed to be doing his best to secure an exit.

But the 24-year-old defender confirmed he would return to training with the Portuguese club on Monday after accepting that he was out of line, telling the club's official website: "It was a misunderstanding and I was hot-headed. I regret what happened, because I feel like I didn't act professionally.

"Now I am going to try and fix the situation. We have spoken, we have understood each other and I am back in training at the Academy."

United turned to Rojo after two of their main defensive targets -- Mats Hummels and Thomas Vermaelen -- eluded them, with Van Gaal keen to reinforce his back line following an opening day home defeat to Swansea.

Sporting terminated the agreement with Doyen after accusing them of conspiring with other clubs to ensure bids came in for Rojo.

Regarding a potential move away from Sporting, Rojo said: "The future depends on the club... if something has to happen, then it should be positive for Sporting and for me. I want to make it clear that I am really happy at Sporting, I like how I am treated and the affection that has been shown for me.

"When I was signed, I wasn't going through a good time and the club trusted me. All I can do is thank Sporting."

And the defender also dismissed an alleged violent incident, adding: "It is all a lie and I was annoyed by how things were just made up."